In this communication age, content providers are increasingly investigating ways in which to provide more content to users as well as interfacing with users.
Communication satellites have become commonplace for use in many types of communication services, e.g., data transfer, voice communications, television spot beam coverage, and other data transfer applications. As such, “bent pipe” satellites transmit and receive large amounts of signals used or “multiple spot beam” configuration to transmit signals to desired geographic locations on the earth. Mobile applications such as telephones and personal digital applications are becoming increasingly popular.
All of these current mobile satellite communication systems, however, suffer from a variety of disadvantages. First, they all have limited frequency resources. Any given frequency over a given ground position can only be utilized by one user with mobile handset at a time. This is true regardless of the sophistication of the system, including systems that utilize multiple beam satellite designs. Even when multiple satellites are available at a given geographic location, the same frequency spectrum cannot be used by more than one nearby mobile handset user. The availability of multiple satellites merely serves to increase the availability of the system to that mobile handset user who is assigned the specific frequency spectrum. However, the total capacity of these mobile communication satellite systems is still limited by the inefficient usage of the frequency spectrum. Thus, the potential growth of these current satellite communication systems is inherently limited.
Additionally, current telecommunications systems only allow mobile-to-hub and hub-to-mobile communications in most of the low earth orbit nd medium earth orbit mobile satellite constellations. Mobile-to-mobile linkages require multiple hops between hubs. Thus, one user with a mobile handset utilizes a satellite at a frequency slot to communicate to his counterpart on the network. Other satellites on or in the same region cannot reuse the same frequency slot for other nearby handset users. Thus, if a secondary user nearby has a handset that requires a particular frequency, which is being utilized by the first user nearby, the second user is unable to access the system through the same frequency via different satellites.
As described in U.S. Pat. No. 5,903,549, satellites may use a phased array antenna to communicate with users on the ground. The phased array antenna is comprised of a plurality of elements that are used to form a beam. The beam forming is implemented by adjusting the amplitude and phase of each signal path routed to each feed element. Each individual signal path is routed to multiple feeds with relative amplitudes and phases, which define each intended beam. In the '549 patent, the beam forming has been removed from the satellite and is performed on the ground. This reduces the complexity of the payload of the satellite.
Implementing a mobile communication system using a satellite is relatively expensive due to the typical complexity of the satellite payload and the expense of launch. The satellites also use a relatively low gain antenna, which is sometimes inadequate for third generation (3-G) cellular type systems. Because of the complexity, the satellites cannot be deployed quickly and thus, from a business standpoint, marketshare may be lost. Also, as new technology develops, the satellite must be replaced which is also very expensive.
The “bandwidth density” over a populate area from a mobile satellite system is limited. It is not cost effective to form multiple beams with beam-widths on the order of 10 Km or less at S-band from satellites. The required aperture is about 1 Km in diameter from a geo-stationary satellite, and hundreds of meters on MEO satellites. However, we can design mobile system using similar techniques but on stratospheric platforms to improve “projected bandwidth density” by thousands of folds.
One limiting factor to the number of users of a system is interference between the various beams. To reduce interference, commonly either the number of users is reduced or the antenna aperture is increased. Maximizing users is a desirable goal. Also, increasing the antenna aperture increases the spacecraft weight which is undesirable.
It would therefore be desirable to provide a mobile communication system that is capable of rapid deployment, is easy to change should the technology inevitably change and reduces the amount of interference with adjacent beams to permit high throughput.